Currently, as the number of communications users increases and new communications standards are increasingly popular, capacity expansion often needs to be performed for a base station to increase a new standard or frequency band, so as to support more users. The CPRI (Common Public Radio Interface, Common Public Radio Interface) protocol is a common interface protocol between a baseband unit (Baseband Unit, BBU) and a radio remote unit (Radio Remote Unit, RRU) in a radio communications base station and used for a connection between a radio equipment control center (Radio Equipment Control, REC) and a radio equipment (Radio Equipment) in a radio base station.
During capacity expansion for a base station, upgrade and reconstruction may be performed on an original base station system, an optical fiber and a power supply are reconstructed, and the optical fiber is directly used to transmit a CPRI signal. However, this manner requires a large amount of engineering reconstruction and costs a lot. Therefore, for the purpose of reducing the costs, an original coaxial line may be used to transmit a CPRI signal, a CPRI electrical signal is directly output, a direct-current power supply and the electrical signal that is converted from a CPRI optical signal are combined by a bias tee and then transmitted to a tower by means of the coaxial line, then the direct-current power supply and an optical signal that is converted from the CPRI electrical signal are separated by the bias tee, and the two parts of signals are transmitted to a device on the tower.
During implementation of the present invention, the inventor finds at least the following problems in the prior art:
Transmitting a CPRI signal using a coaxial line occupies extremely high bandwidth; as a result, remaining frequency resources for other services to use are extremely few in the coaxial line; therefore, frequency resource utilization is not high.